Abstract

We used differential screening to isolate ripening-associated cDNAs from a Shiraz grape (Vitis vinifera L.) berry cDNA library. A rapid increase in the mRNA levels of a number of cDNAs not present in unripe fruit occurred in grape berries at the onset of ripening. The putative translation products of some of these clones had homologs in other species that are involved in cell wall structure. These included four proline-rich proteins, a small protein that is similar to the non-catalytic, N-terminal domain of some pectin methylesterases, and two other glutamate-rich proteins. The remainder of the clones encoded putative stress response proteins. These included two thaumatin-like proteins, a metallothionein, a transcription factor, a cytochrome P450 enzyme, and proteins induced by water, sugar, and/or cold stress in other species. Many of the homologs of the grape cDNAs thought to be involved in cell wall structure or stress-related responses also accumulate in a developmental manner in other plants. This may indicate that the grape mRNAs accumulate in response to stresses such as the storage of high concentrations of sugars and rapid cell expansion, or they may accumulate as part of the ripening developmental program.

Northern-blot analysis of the expression of Grip clones (and the gfh2 and VvTL2 clones) in various grape tissues. RNA from root (R), young leaf (Y), mid leaf (M), old leaf (O), seed from berries 4 wpf (S), flower (F), and a series of samples taken from developing berries at two weekly intervals (commencing at 2 wpf) were probed with the cDNAs as indicated. The dashed line indicates véraison. A, Genes exhibiting berry- and ripening-specific expression. B, Genes with up-regulated expression during ripening but also expressed in other tissues. CW, Clones encoding putative cell wall proteins. The bottom panel is a photograph of an ethidium-bromide-stained gel to show the intactness and relative loadings of the RNA samples used in the northern analysis.